Generally, a squirrel-cage motor is started by closing the stator circuit power switch. However, because of the large-starting current surge, a squirrel-cage motor can not usually be started in this straightforward manner. The large current surge may produce such a large voltage swing that the operation of the electric equipment, connected to the same supply network (especially lamps), is disturbed. This is the main reason why there have been developed several techniques for starting a squirrel-cage motor, which are designed to reduce the starting current. Conventionally, the starting current is reduced e.g. by using star-delta starting or by connecting starting resistances between the stator and the supplying network.
However, star-delta starting cannot be used in all situations because there are relatively large transient changes in the current at the moment of switching from star to delta connection. Especially in weak networks, these current variations may cause disturbances in functioning of the electric equipment connected to the network, e.g. blinking of lamps, just as the above-described direct starting does. Again, the use of starting resistances requires the installation of extra resistors.
U.S. Pat. No. 4,417,192 (Ghosh) and EP 0205877 (Ghosh) present different winding systems for starting. These winding systems apply to motors having a given number of pole pairs and certain q-values (number of slots per pole and phase). Therefore, for example in the case of motors with single layer windings, it is impossible to use one winding coil per pole and phase with these systems.